How To Assign Output of a Linux Command to a Variable

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When you run a command, it produces some kind of output: either the result of a program is suppose to produce or status/error messages of the program execution details. Sometimes, you may want to store the output of a command in a variable to be used in a later operation.

In this post, we will review the different ways of assigning the output of a shell command to a variable, specifically useful for shell scripting purpose.

To store the output of a command in a variable, you can use the shell command substitution feature in the forms below:

variable_name=$(command)
variable_name=$(command [option ...] arg1 arg2 ...)
OR
variable_name='command'
variable_name='command [option ...] arg1 arg2 ...'

Below are a few examples of using command substitution.

In this first example, we will store the value of who (which shows who is logged on the system) command in the variable CURRENT_USERS user:

$ CURRENT_USERS=$(who)

Then we can use the variable in a sentence displayed using the echo command like so:

$ echo -e "The following users are logged on the system:/n/n $CURRENT_USERS"

In the command above: the flag -e means interpret any escape sequences ( such as /n for newline) used. To avoid wasting time as well as memory, simply perform the command substitution within the echo command as follows:

$ echo -e "The following users are logged on the system:/n/n $(who)"
How To Assign Output of a Linux Command to a Variable

Shows Current Logged Users in Linux

Next, to demonstrate the concept using the second form; we can store the total number of files in the current working directory in a variable called FILES and echo it later as follows:

$ FILES=`sudo find . -type f -print | wc -l`
$ echo "There are $FILES in the current working directory."
How To Assign Output of a Linux Command to a Variable

Show Number of Files in Directory

That’s it for now, in this article, we explained the methods of assigning the output of a shell command to a variable. You can add your thoughts to this post via the feedback section below.

Source: tecmint.com

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